Benson said CAS can deliver a minimum of 8 Mbps over ordinary lines with no extra carrier services or equipment needed and no distance limitations between sender and receiver. 'We've demonstrated up to 16 Mbps,' he said.

Other companies may manufacture and distribute the equipment under their brands as early as this winter, Benson said. He said there are potential users at government agencies.''Like everyone else we talked to, they said, 'If you can do that, we're interested,' ' Benson said.

Prototype tests so far have been limited to transmissions over Washington-area telephone networks. Benson said tone frequency modulation transmits acoustic pulses over copper telephone lines much as wave-division multiplexing transmits light frequencies over fiber-optic cable. Although tone frequency modulation does require a digital-to-analog conversion, the signal moves in pulses rather than analog waveforms, boosting data density and therefore transmission speed.

Because the signals are acoustic, the public telephone network treats them as voice transmissions, and no central office service or equipment is needed'only a board on each sending and receiving computer. Neither line quality nor distance from a central office limits the transmission rates, Benson said.